[petsc-users] about linear solver convergence

[Jack Poulson]

On Tue, Oct 11, 2011 at 11:15 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Oct 11, 2011 at 11:13 AM, behzad baghapour <
> behzad.baghapour at gmail.com> wrote:
>
>> Okey. I checked the condition number "max/min".
>> It increases significantly in each ksp iterations!!!
>>
>
> The approximation is becoming better. The condition number is harder to
> actually compute than the solution.
>
> Bottom line: You have a hard problem. Iterative methods do not work on hard
> problems without specialized
> preconditioners. I recommend a literature search on solvers for your
> equations.
>
>
>From what he said earlier,

> I have solved my problem before with some other solvers (gmers/ILU(2)) and
the
> convergence has been achieved within 15 - 16 iterations.

it sounds like he should try using one of Hypre's ILUs.
http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-dev/docs/manualpages/PC/PCHYPRE.html

Bezhad, why start with Jacobi if you already knew that GMRES+ILU(2) works?

Jack
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